Polarographic oxygen sensors are well-known in medical technology. In operation, such a sensor determines the transfer rate of oxygen through a diffusion barrier by measuring the related limiting reduction current at a polarized electrode. A monitoring system would conventionally include a sensor head having an anode and a cathode exposed to an electrochemically active surface. The sensor head has a lead cable extending from it and adapted to be connected to an amplifier in the system. Current supplied from the amplifier normally maintains the electrode in a polarized state.
The sensor head and cable are readily detachable from the amplifier. In normal operation they might be used on patient monitoring for a period of time and then detached from the monitoring system amplifier for use on another patient in another system. They might also be stored temporarily. In any case, detaching the sensor head and cable from the system causes the head to become depolarized and, prior to its reuse, it must be repolarized. Repolarization requires up to two hours as a result of which the sensor can't be used again immediately.